EP 1 229 985 B1 discloses a generic liquid filter having a filter housing which is arranged essentially vertical when in the installed state and which contains a receiving space for a ring filter element inserted therein for filtering a liquid. The ring filter element is matched to the filter housing in such a manner that it can be freely rotated about its longitudinal axis in the receiving space as long as a pin projecting axially and eccentrically from the lower end disc of the ring filter element does not engage in an opening of a no-load duct. A ramp is formed on the bottom of the receiving space, which ramp starts on the bottom with a lower end at the opening of the no-load duct and rises with increasing ramp length into the interior of the receiving space. When the ring filter element is inserted into the filter housing, the pin lies on the ramp and slides down along it when the ring filter element is rotated, penetrating the opening of the no-load duct at the lower end of the ramp. This embodiment requires the use of a very specific ring filter element, namely one having a pin of this type, because if conventional ring filter elements without the pin are used there would be a short circuit connection between the no-load duct and the inlet or outlet and therefore there would no longer be any functionality.